Aluminum Extrusion Alloy

ABSTRACT

An aluminum alloy includes Si and Mg in amounts (wt. %) within a quadrilateral defined by the following coordinates on an Mg/Si plot: I: 1.15 Si, 0.70 Mg, II: 0.95 Si, 0.55 Mg; III: 0.75 Si, 0.65 Mg; and IV: 0.95 Si, 0.85 Mg. The alloy also includes, in weight percent: Mn 0.40-0.80 Fe 0.25 max Cr 0.05-0.18 Cu 0.30-0.90 Ti 0.05 max Zr 0.03 max Zn 0.03 max B 0.01 max with the remainder of the alloy being aluminum and unavoidable impurities in amounts of up to 0.05 wt. % each and 0.15 wt. % total.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to, and the benefit of, U.S.Provisional Application No. 62/774,661, filed Dec. 3, 2018, which priorapplication is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

This disclosure relates to aluminum alloys suitable for use inextrusion, and more specifically in one aspect to Al—Mg—Si—Cu—Mn—Crextrusion alloys having high strength and ductility.

BACKGROUND

Aluminum extrusion alloys are often used for automotive applications,and higher strength extrusion alloys having yield strengths of at least350 MPa are sometimes desired or needed for this purpose. A number ofexisting commercial alloys are capable of this strength level, such asAA6066 and AA6056, but these alloys exhibit decreased extrudabilitycompared to standard extrusion alloys. Ductility and crush performancecan also be an issue in such higher strength alloys. Thus, there is aneed for an aluminum extrusion alloy capable of consistently achieving ayield strength of 350 MPa or greater, with good extrudability andductility. In order to ensure that an alloy in commercial productionconsistently meets a minimum yield strength, it is desirable that theaverage or typical yield strength value should significantly exceed theminimum target, such as by at least 20 MPa, to account for variations instrength from sample to sample. For example, to ensure that a targetedminimum strength of 350 MPa is consistently met, an average yieldstrength of 370 MPa or more would be desired.

The present disclosure is provided to address this need and other needsin existing aluminum extrusion alloys. A full discussion of the featuresand advantages of the present invention is deferred to the followingdetailed description, which proceeds with reference to the accompanyingdrawings.

BRIEF SUMMARY

Aspects of the disclosure relate to an aluminum extrusion alloy thatincludes Si and Mg in amounts within a quadrilateral defined by thefollowing coordinates on an Mg/Si plot, in weight percent:

I 1.15 Si, 0.70 Mg II 0.95 Si, 0.55 Mg III 0.75 Si, 0.65 Mg IV 0.95 Si,0.85 Mgwherein the alloy further comprises, in weight percent:

Mn 0.40-0.80 Fe 0.25 max Cr 0.05-0.18 Cu 0.30-0.90 Ti 0.05 max Zr 0.03max Zn 0.03 max B 0.01 max

with the remainder of the alloy being aluminum and unavoidableimpurities in amounts of up to 0.05 wt. % each and 0.15 wt. % total.

According to one aspect, the Mg and Si are present in an Mg/Si ratio ofat least 0.69 and/or no more than 0.88.

According to another aspect, the alloy includes excess Mg, and in oneembodiment, up to 0.40 wt. % excess Mg as defined herein.

According to a further aspect, the alloy, after homogenization,extrusion, and artificial ageing, has a predominantly non-recrystallizedmicrostructure.

According to yet another aspect, after homogenization, extrusion, andartificial ageing, has a yield strength of at least 350 MPa and atensile elongation of at least 8%. The alloy may have a yield strengthof at least 370 MPa in one embodiment.

According to a still further aspect, the alloy includes Mg in an amountof 0.60-0.80 wt. % and Si in an amount of 0.85-1.10 wt. %. In oneembodiment, the Mg content may be 0.70-0.80 wt. % and the Si content maybe 0.85-0.95 wt. %.

According to yet another aspect, the Si and Mg in amounts are within aquadrilateral defined by the following coordinates on the Mg/Si plot, inweight percent:

I 1.15 Si, 0.70 Mg II 0.95 Si, 0.55 Mg III′: 0.80 Si, 0.65 Mg IV′: 0.95Si, 0.80 Mg.

Additional aspects of the disclosure relate to an aluminum extrusionalloy that includes, in weight percent:

Mg 0.60-0.80 Si 0.85-1.10 Mn 0.40-0.80 Fe 0.25 max Cr 0.05-0.18 Cu0.30-0.90 Ti 0.05 max Zr 0.03 max Zn 0.03 max B 0.01 max

with the remainder of the alloy being aluminum and unavoidableimpurities in amounts of up to 0.05 each and 0.15 total. The alloy mayinclude any other aspects discussed above herein.

Further aspects of the disclosure relate to an extruded product that isat least partially formed of an aluminum alloy as described herein.

Still further aspects of the disclosure relate to a method that includescasting or otherwise forming a billet of an aluminum alloy as describedherein, e.g., using direct chill casting or other continuous castingtechnique, then homogenizing the billet and extruding the homogenizedbillet to form an extruded product. The homogenization may be conductedby heating the billet at a temperature of 540-580° C. for 2-10 hours,and then cooling the billets at a cooling rate of 300° C./hour or moreafter homogenization.

Other features and advantages of the disclosure will be apparent fromthe following description taken in conjunction with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

To allow for a more full understanding of the present disclosure, itwill now be described by way of example, with reference to theaccompanying drawings in which:

FIG. 1 illustrates magnesium and silicon content of embodiments of analuminum alloy according to aspects of the disclosure;

FIG. 2 illustrates a plot of crush rating and fracture strain vs. yieldstrength for several alloys tested in Examples 1 and 2 herein;

FIG. 3 illustrates a plot of mean crush force vs. yield strength forseveral alloys tested in Examples 1 and 2 herein;

FIG. 4 illustrates a plot of ram pressure vs. yield strength for severalalloys tested in Example 2 herein; and

FIG. 5 illustrates magnesium and silicon content of embodiments of analuminum alloy according to aspects of the disclosure, as well asexample compositions tested in Example 5 herein.

DETAILED DESCRIPTION

While this invention is susceptible of embodiments in many differentforms, there are shown in the drawings and will herein be described indetail example embodiments of the invention with the understanding thatthe present disclosure is to be considered as an exemplification of theprinciples of the invention and is not intended to limit the broadaspect of the invention to the embodiments illustrated. It is to beunderstood that other specific arrangements features may be utilized andmodifications may be made without departing from the scope of thepresent invention.

Aspects of the disclosure relate to an aluminum alloy that is useful forextrusion applications, having various alloying elements including Mg,Si, Fe, Mn, Cu, and Cr. An alloy as described herein may also be usefulin forging applications, and may produce beneficial properties in suchan application. All composition percentages listed herein are in weightpercent unless otherwise indicated.

In one embodiment, the alloy may include magnesium in an amount of0.60-0.80 wt. %, or 0.6-0.8 wt. %, and silicon in an amount of 0.85-1.10wt. %. The Mg and Si in this composition may also be present in an Mg/Siratio (wt. %) of at least 0.69 in one embodiment. The Mg/Si ratio mayadditionally or alternately have an upper limit of 0.88 in oneembodiment or 0.85 in another embodiment. Alloys with Mg/Si ratios thatare too high can be detrimental to extrudability in amounts, and alloyswith Mg/Si ratios above these amounts may exhibit unsatisfactoryextrudability. In another embodiment, the alloy may include magnesium ina range of 0.70-0.80 wt. % and silicon in a range of 0.85-0.95 wt. %.

In another embodiment, the alloy may include magnesium and silicon inamounts defined within a quadrilateral defined by the followingcoordinates on a Mg/Si plot, as shown in FIG. 1:

I: 1.15 Si, 0.70 Mg

II: 0.95 Si, 0.55 Mg

III: 0.75 Si, 0.65 Mg

IV: 0.95 Si, 0.85 Mg

The alloy in a further embodiment may include magnesium and silicon inamounts defined within a quadrilateral defined by the followingcoordinates on an Mg/Si plot, as shown in FIG. 1:

I: 1.15 Si, 0.70 Mg

II: 0.95 Si, 0.55 Mg

III′: 0.80 Si, 0.65 Mg

IV′: 0.95 Si, 0.80 Mg

In any of the embodiments herein, the alloy may include at least someexcess magnesium (i.e., excess Mg>0) as defined by the equation below:

Excess Mg=Mg−(Si−(Mn+Fe+Cr)/3)/1.16 (all values in wt %)

The alloy may include up to 0.40 wt. % excess magnesium in oneembodiment, and up to 0.35 wt. % excess magnesium in another embodiment.Excess Mg can be detrimental to extrudability in amounts that are toohigh, and alloys with excess Mg above these amounts may exhibitunsatisfactory extrudability.

The alloy may further contain the following elements, in wt. %:

Mn 0.40-0.80 Fe 0.25 max Cr 0.05-0.18 Cu 0.30-0.90 Ti 0.05 max Zr 0.03max Zn 0.03 maxwith the remainder of the alloy being aluminum and unavoidableimpurities, which may be present in amounts of up to 0.05 wt. % each and0.15 wt. % total. In one embodiment, the alloy may include additionalelements not listed.

Silicon can combine with iron, manganese, and/or chromium inintermetallic phases in the alloy. Additionally, manganese and chromiumin sufficient amounts can form dispersoid particles that inhibit grainrecrystallization after extrusion. The iron content of the alloy in oneembodiment is 0.25 wt % max. In another embodiment, the iron content ofthe alloy may be 0.15-0.25 wt. %. The chromium content of the alloy inone embodiment is 0.05-0.18 wt. %. In another embodiment, the chromiumcontent of the alloy may be 0.05-0.15 wt. %. The manganese content ofthe alloy in one embodiment is 0.40-0.80 wt. %, but may alternately be0.4-0.8 wt. %. In another embodiment, the manganese content of the alloymay be 0.40-0.55 wt. %.

Copper can increase strength of the alloy. The copper content of thealloy in the embodiment listed above is 0.30-0.90 wt %, but mayalternately be 0.3-0.9 wt. %. In other embodiments, the copper contentof the alloy may be 0.30-0.80 wt. %, 0.60-0.80 wt. %, or 0.60-0.90 wt.%.

Titanium is added as a grain refiner in one embodiment, and may be addedalong with boron in the form of TiB rod (e.g., 5% Ti, 1% B).Accordingly, the alloy may also include up to 0.01% or up to 0.005%boron in one embodiment.

Alloys according to aspects and embodiments herein may be prepared byforming into billets through direct chill casting or other continuouscasting method in one embodiment, and then homogenizing the billets.Homogenization may be performed, for example, at 540-580° C. for 2-10hours, and then cooling the billets at 300° C./hour or more, e.g.,300-600° C./hour, after homogenization. It is understood that thesecooling rates may be measured over a portion of the cooling range, andnot throughout the entire cooling of the billet (i.e., homogenizationtemperature to ambient temperature). For example, in one embodiment, therelevant cooling rate may be measured between the temperatures of 500°C. and 200° C. during cooling. The billets may then be extruded into anextrusion profile or extruded product, which may include at least oneconcave surface, at least one convex surface, at least one angledcorner, and/or at least one internal cavity in some uses. Extrusion maybe performed in one embodiment by preheating to 470-520° C. prior toextrusion and water quenching at the press exit, e.g., by water spraysor a standing wave water box, which may achieve cooling at about50-1000° C./sec. The extruded product may be subjected to artificialageing after extrusion, such as heating for 5-16 hours at 160-185° C. Itis understood that other processing may be used in other embodiments,including post-extrusion processing to the extruded product to achievedesired properties, geometry, etc.

The extruded product produced using the alloys and processing techniquesdescribed herein may have a post-extrusion grain structure that ispredominantly fibrous or non-recrystallized in one embodiment. Thispredominantly fibrous microstructure may have a microstructure that isat least 50% unrecrystallized in one embodiment, or at least 75%unrecrystallized in another embodiment, which may be over a majority ofthe length of the extruded profile or over the entire length. Anon-recrystallized grain structure may improve the yield strength of thealloy after extrusion. In one embodiment, an alloy as described hereinmay achieve a yield strength of at least 350 MPa or at least 360 MPa,with a tensile elongation of at least 8%, at least 9%, or at least 10%,after extrusion and artificial ageing.

Below are several examples illustrating the beneficial properties andadvantageous performance of alloys according to aspects of thedisclosure, as well as comparative alloys.

Example 1

The alloy compositions listed in Table 1, representing existingcommercial high strength AA 6XXX alloys, were direct chill cast as 101.6mm diameter ingots, and a 5% Ti-1% B grain refiner was added prior tocasting to ensure a fine as-cast grain size.

TABLE 1 Commercial Alloy Compositions type Si Fe Cu Mn Mg Cr V Zr Ti B6111 0.66 0.20 0.70 0.20 0.70 0.00 0.01 <001 0.02 0.002 6056 0.96 0.180.56 0.79 0.67 0.00 0.01 0.10 0.02 0.002 6066 1.26 0.20 0.76 0.45 0.870.09 0.01 <.001 0.00 0.001

The ingots were cut into 400 mm billet lengths and homogenized. Thebillets of AA6111 and AA6056 were homogenized for 2 hours at 560° C.,and the AA6066 billet was homogenized for 4 hours at 545° C. The billetswere cooled at 400° C./hr after homogenization.

The billets were extruded into a 40×30×2 mm hollow profile with a 5 mmexternal corner radius using a billet temperature of 475° C. and a ramspeed of 4-6 mm/s. The ram speed was varied to find the maximum speedattainable before surface cracking occurred. This maximum ram speed isreported in Table 2. The extrusion ratio was 32/1, such thatcorresponding exit speeds ranged from 8-12 m/min. The extrusion waswater quenched at a rate of ˜1000° C./sec using a standing wave waterquench unit positioned about 2.5 m from the extrusion die. Theextrusions were floor aged at room temperature for 24 hours beforeartificial ageing for 8 hrs/175° C.

Crush tests were performed by axially crushing a 150 mm length to 30 mmat a cross head speed of 20 mm/s. The load displacement curve wasrecorded and the mean crush force (MCF) was calculated using anaveraging technique. The extent of cracking (crush rating CR) during thecrush test was assessed on a scale of 1 to 9, where 1 represented acrack free sample and 9 represented full disintegration. Longitudinaltensile testing was performed, the area of the final fracture wasmeasured, and the true fracture strain was calculated as e_(f)=−Ln(final area/initial area). The true fracture strain (e_(f)) has beenshown to be a good measurement of ductility at high plastic strains. Themechanical property and crush testing results are also reported in Table2, where RX signifies a fully recrystallized grain structure and Fsignifies a predominantly fibrous grain structure. Some of these resultsare also depicted graphically in FIGS. 2-3.

TABLE 2 Mechanical Properties max ram YS UTS MCF grain speed Alloy MPaMPa % EI ef kN C.R structure mm/s 6111 338 367 12 0.6 33.1 3 RX >6 6056384 403 11 0.4 36.4 8 F 5 6066 417 443 12 0.2 33 9 F 4

The AA6066 alloy exhibited the lowest extrusion speed, followed by theAA6056 alloy. The AA6111 alloy had the highest maximum ram speed, andwas the most extrudable of the three alloys. AA6111, which is widelyused as an automotive sheet alloy, resulted in a fully recrystallizedgrain structure and did not meet the 350 MPa minimum yield strengthtarget. Both the AA6056 and AA6066 alloys exhibited yield strengths inexcess of the 350 MPa target, along with a predominantly fibrous ornon-recrystallized grain structure. However, the higher strengths ofthese alloys did not translate into increased energy absorption, andAA6056 and AA6066 both performed poorly in crush testing. In particular,the AA6066 alloy experienced premature onset of cracking in the crushtest and had a low fracture strain.

Example 2

The alloys listed in Table 3 were direct chill cast as 101.6 mm diameteringots and cut into 400 mm billet lengths, and a 5% Ti-1% B grainrefiner was added prior to casting to ensure a fine as-cast grain size.

TABLE 3 Alloy Compositions type Si Fe Cu Mn Mg Cr V Zr Ti B A 0.87 0.15<.001 0.50 0.64 0.13 0.01 <.001 0.003 0.0003 B 0.91 0.18 0.01 0.50 0.640.14 0.12 <.001 0.010 0.002 C 0.90 0.16 0.32 0.51 0.66 0.12 0.01 <.0010.020 0.007 D 0.89 0.17 0.61 0.49 0.68 0.13 0.01 <.001 0.007 0.001 E0.90 0.17 0.30 0.07 0.64 0.00 0.01 <.001 0.012 0.002 F 0.88 0.17 0.300.77 0.64 0.14 0.01 0.001 0.014 0.002

The billets were homogenized for 2 hours at 550° C. and cooled at 400°C./hour after homogenization. The billets were extruded into a 40×30×2mm hollow profile using a billet temperature of 500° C. and a fixed ramspeed of 5 mm/s. The extrusion was water quenched at a rate of ˜1000°C./sec using a standing wave water quench unit positioned about 2.5 mfrom the extrusion die. The extrusions were floor aged at roomtemperature for 24 hours before artificial ageing for 8 hours at 175° C.Tensile and crush testing was performed, the extrusion hydraulicpressure was monitored and the maximum (breakthrough) pressure value andthe value at 50% of the ram stroke were extracted. The percentagedifference in breakthrough pressure compared to alloy A (ΔP) wascalculated to give an indication of the relative extrudability. Theincrease in yield strength per each % increase in extrusion pressurecompared to alloy A was also calculated to assess the strengtheningefficiency as compared to the effect on extrudability. The test resultsare summarized in Table 4, where RX signifies a fully recrystallizedgrain structure and F signifies a predominantly fibrous grain structure.Some of these results are also depicted graphically in FIGS. 2-4.

TABLE 4 Mechanical Properties YS UTS MCF grain YS per inc. P ΔP AlloyMPa MPa % EI ef kN C.R structure MPa/% P % A 312 331 10.7 0.73 29.92 3 F. . . . . . B 311 329 10.9 0.73 29.11 2 F −0.20 4.9 C 361 377 11.1 0.5733.75 5 F 27.57 1.8 D 379 403 11.8 0.54 35.57 4 F 11.28 5.9 E 346 3609.9 0.28 28.91 9 RX −2.56 −13.3 F 348 369 11.2 0.54 32.35 2 F 5.22 6.9

Alloy A, which is used for comparative purposes, is based on anautomotive grade AA6082, gave good ductility and a good crush rating,but only achieved a yield strength of 312 MPa. The alloy containedadditions of Mn and Cr to form submicron dispersoid particles duringhomogenization and this resulted in a predominantlyfibrous/non-recrystallized grain structure after extrusion. Alloy B,with a V addition relative to Alloy A, exhibited similar strength andductility with a small (1 grade) improvement in crush rating. Alloy C,with an addition of 0.32% Cu relative to Alloy A, exhibited a yieldstrength in excess of the 350 MPa target with some deterioration inductility as measured by the fracture strain and crush rating. Alloy D,with an addition of 0.61% Cu relative to Alloy A, exhibited an excellentyield strength of 379 MPa with only slightly lower fracture strain andinferior crush rating to Alloy C. Alloy E, with an addition of 0.30% Curelative to Alloy A, but no addition of Cr and only 0.07% Mn, resultedin a recrystallized grain structure. While Alloy E only exhibited ayield strength of 346 MPa, it also gave the lowest fracture strain andhighest (worst) crush rating of 9, representing full disintegration.Finally, Alloy F, which was similar to alloy C but with the Mn contentincreased to 0.77, gave slightly lower strength than alloy C, nearlymeeting the 350 MPa target, but a significantly better crush rating.

The fracture strain and crush rating results for Examples 1 and 2 areplotted in FIG. 2 as a function of the yield strength. From examinationof this plot, it is apparent that Alloys C and D offer a yield strengthin excess of 350 MPa and reasonable ductility in terms of crush ratingand fracture strain. Although the existing commercial alloys AA6066 andAA6056 are capable of higher strengths, this increased strength isaccompanied by a significant deterioration in fracture strain and crushrating relative to Alloys C and D. The results for the other alloyvariants would suggest that a predominantly fibrous (non-recrystallized)grain structure is preferred, and that reduced levels of Mn and theabsence of Cr, as in the case of Alloy E, are undesirable. The improvedcrush rating and reasonably high yield strength for Alloy F suggeststhat increasing the Mn level to about 0.8% in addition to the Craddition could also be beneficial.

FIG. 3 shows a similar plot for MCF vs. yield strength for the alloys inExamples 1 and 2. In general, the MCF increases in line with the yieldstrength, with the exception of Alloys E and AA6066, due to theirreduced ductility and premature failure in the crush test. Similarconclusions can be drawn from the data in FIGS. 2 and 3.

FIG. 4 shows the extrusion pressure results for the breakthroughpressure (upper curve) and the pressure at mid stroke (lower curve),again plotted against the yield strength to give an indication of thepenalty in extrudability incurred by increasing the alloy strength.Adding extra solute to an alloy to gain extra strength from artificialageing would be expected to increase the high temperature flow stress,making the alloy more difficult to extrude. In general, the higher theextrusion pressure of an alloy, the lower the maximum extrusion speedthat can be achieved for a given billet temperature. Using Alloy A asthe baseline, FIG. 4 indicates that Alloy E was the only variant toexhibit lower extrusion pressure than the base alloy. However, asdescribed above, this also corresponded to significantly inferiorductility. Alloy B, containing the V addition, required ˜ 5% higherbreakthrough pressure than Alloy A, with no corresponding increase inyield strength. Alloys C and D required extrusion pressure increases of1.8 and 5.9% respectively for useful yield strength increases of 49 and67 MPa relative to Alloy A. Alloy F required a 6.90% increase inbreakthrough pressure for a yield strength gain of 36 MPa relative toAlloy A. When the yield strength increase per % increase in breakthroughpressure values are compared in Table 4, it is clear that alloys C and Dcontaining additions of about 0.3 and 0.6 Cu are the most efficient interms of achieving the target strength level with minimum loss ofextrudability.

Example 3

The alloy compositions G and H shown in Table 5 were direct chill castas 228 mm diameter ingots, cut into billets, homogenized for 2 hours at560° C., and cooled at 450° C./hour after homogenization. Five billetsof each alloy were extruded on a commercial extrusion press into atwo-cavity bumper profile with wall thicknesses varying between 2.6 and3.6 mm. A billet preheat temperature of 500° C. was used with a ramspeed of 3 mm/s. The profile was spray water quenched and artificiallyaged for 8 hours at 175° C. Alloys G and H contained Cu, Mn, and Crcontents similar to those of Alloy D from Example 2, but the Mg and Sicontents of these alloys were increased relative to Alloy D. Tensiletesting was conducted on the top and bottom of the profile, and theresults are shown in Table 5.

TABLE 5 Alloy Compositions and Mechanical Properties YS (MPa) UTS (MPa)% EI Alloy Si Fe Cu Mn Mg Cr V Zr Ti B top bottom top bottom top bottomG 0.91 0.18 0.70 0.60 0.79 0.12 0.014 0.001 0.03 0.002 383 363 416 39912.2 10 H 1.01 0.17 0.58 0.60 0.70 0.14 0.016 0.001 0.03 0.004 378 360406 392 12.4 10.6

The grain structure was checked by optical metallography, and allextrusions had a predominantly fibrous/non-recrystallized grainstructure. The strength of both Alloys G and H varied between the topand bottom locations, most likely due to variations in quench rateassociated with the spray quench settings. Both alloys achieved yieldstrengths of 360 MPa or greater for the bottom locations with the lowerquench rate and near or exceeding 380 MPa at the faster quenched toplocation.

Example 4

Alloy I, shown in Table 6, was direct chill cast as 101.6 mm ingots andcut into billets. The billets were homogenized for 2 hours at 560° C.and cooled at 450° C./hour after homogenization, and were then extrudedinto a 50×2.5 mm strip using a billet temperature of 500° C. and a ramspeed of 5 mm/s. The extrusion was water quenched at a rate of 1000°C./sec at the press exit and then artificially aged for 8 hours at 175°C. After this treatment, Alloy I achieved a yield strength of 391 MPa,an ultimate tensile strength of 419 MPa, and 12.7% elongation in tensiletesting.

TABLE 6 Alloy Composition Si Fe Cu Mn Mg Cr V Zr Ti B I 0.93 0.17 0.630.48 0.73 0.14 0.013 <.001 0.03 0.002

Alloy J, shown in Table 7, was direct chill cast as 254 mm diameterbillet and homogenized for 3 hours at 560° C. and cooled at 400° C./hourafter homogenization.

TABLE 7 Alloy Composition Si Fe Cu Mn Mg Cr V Zr Ti B J 0.94 0.17 0.630.71 0.73 0.13 0.010 0.001 0.03 0.003

This billet was extruded on a commercial press into a bumper profilewith an extrusion ratio of 50.1 and wall thicknesses from 2.5 to 5 mmusing a billet temperature of 490° C. and an exit speed of 8 m/min. Theprofile was spray quenched at the press exit. After artificial ageingfor 8 hours at 175° C., Alloy J achieved a yield strength of 395 MPa, anultimate tensile strength of 421.9 MPa, and an elongation of 10.4%.

Example 5

The alloy compositions listed in Table 8 were direct chill cast as 101.6mm ingots and cut into 200 mm billet lengths. The billets were grainrefined using a 5% Ti-1% B grain refiner added prior to casting. Thebillets were homogenized for 3 hours at 560° C. and cooled at 400°C./hour, with the exception of alloy M, which had a lower equilibriumsolidus and as a result was homogenized for 3 hours at 545° C. to avoidmelting, followed by cooling at 400° C./hour. Groups of 6 billets ofeach alloy were extruded into 3×42 mm profiles with sharp corners, usinga billet temperature of 480° C. The ram speed for each group wasincreased incrementally on successive billets from 4 mm/s to 9 mm/suntil speed cracking was observed at the corners, and, based on thisobservation, the maximum extrusion speed (Vt) without tearing wasestablished. The extrusions were water quenched at the press exit usinga standing wave water quench unit giving a quench rate of ˜1000° C./sec.The maximum breakthrough pressure was recorded during extrusion. Lengthsof extrusion were then aged for 8 hours at 175° C. and tensile testingwas performed. Table 8 presents the results for each alloy in terms oftearing speed (Vt), yield strength (YS), ultimate tensile strength(UTS), breakthrough pressure (Pmax). FIG. 5 illustrates the Mg and Sicompositions of Alloys G-M in Table 6 as compared to the Mg/Si plotsI-IV and I-IV′ as shown in FIG. 1 and the ranges of 0.60-0.80 wt. % Mgand 0.85-1.10 wt. % Si described in the specification. As shown in FIG.5, Alloys G, H, I, and J are within these ranges, and Alloys K, L, and Mare outside these ranges.

TABLE 8 Alloy Compositions and Test Results Vt YS UTS Pmax alloy Si FeCu Mn Mg Cr V Zr Ti B mm/s MPa MPa psi ΔP % G 0.92 0.15 0.66 0.47 0.660.08 0.01 <.001 0.034 0.001 6.5 373 405 1512 −4.8 H 1.05 0.19 0.64 0.440.64 0.08 0.01 <.001 0.035 0.002 3.8 372 408 1491 −6.1 I 0.90 0.16 0.630.46 0.75 0.08 0.01 <.001 0.033 0.001 6 381 412 1588 0.0 J 1.02 0.160.65 0.46 0.75 0.08 0.01 <.001 0.033 0.002 3.8 379 421 . . . . . . K 072 0 16 0 64 0 46 0 64 0 08 0.01 <.001 0.035 0.0017 7 352 383 1528 −3.8L 0.79 0.17 0 65 0 48 0.83 0.08 0.01 <.001 0.034 0.0015 6 367 398 16212.1 M 1.14 0.16 0.64 0.46 0.65 0.08 0.01 <.001 0.034 0.0016 3.5 360 404. . . . . .

Alloys G, H, I and J all achieved yield strength levels in excess of 370MPa, meeting and comfortably exceeding the target strength of 350 MPa.Alloys H and J have higher Si contents, and these alloys exhibitedsignificantly lower tearing speeds than alloys G and I. Alloy I achievedthe best combination of high strength and high extrusion speed of thealloys tested in this Example. Table 8 shows the % breakthrough pressureincrease or decrease (ΔP %) compared to Alloy I. Extrusion pressurevalues are not shown for alloys J and M, as these alloys could not beextruded at comparable speeds to the other alloys.

Alloys K, L, and M have compositions outside the Mg/Si plot I-IV asshown in FIG. 1, and these alloys all exhibited lower yield strengthsthan Alloys G, H, I, and J that fall within the Mg/Si plot I-IV. Alloy Khas a lower Si content such that the composition is outside the Mg/Siplot I-IV as shown in FIG. 1, and this alloy achieved a yield strengthof only 352 MPa. The yield strength of Alloy K is insufficiently inexcess of the target strength of 350 MPa to ensure that the targetstrength is consistently met in a production alloy, indicating a Sicontent higher than 0.72 wt. % achieves superior results. Alloy M hasthe highest silicon content such that the composition is outside theMg/Si plot I-IV as shown in FIG. 1. Alloy M exhibited the lowest tearingspeed, indicating that Alloy M is inferior for extrusion. Additionally,Alloy M exceeded the target strength of 350 MPa by only 10 MPa, and theyield strength of Alloy M is insufficiently in excess of the targetstrength of 350 MPa to ensure that the target strength is consistentlymet in a production alloy. The loss in extrudability and strength inAlloy M compared to Alloys G, H, I and J indicate that a lower siliconcontent than 1.14 wt. % achieves superior results. Alloy L has a high Mgcontent such that the composition is outside the Mg/Si plot I-IV asshown in FIG. 1. Alloy L exhibited generally acceptable strength andtearing speed. However, Alloy L still exhibited lower strength thanAlloys G, H, I, and J, in addition to higher extrusion pressure (andtherefore inferior extrudability) compared to Alloys G, H and I. Thus,under commercial extrusion conditions, the extrusion speed of Alloy Lcould be further restricted by the need to increase the billettemperature to reduce extrusion pressure. Alloy L therefore represents acombination of Mg and Si that exhibits an inferior combination ofstrength and extrudability compared to alloys that are within the Mg/Siplot I-IV as shown in FIG. 1 (e.g., Alloys G, H, and I).

Based on the strength and extrudability performance of alloys G, H, I,and J in this test, it has been demonstrated that the ranges of Mg andSi in the Mg/Si plot I-IV as shown in FIG. 1 and the ranges of 0.60-0.80wt. % Mg and 0.85-1.10 wt. % Si described in the specification canprovide yield strength levels comfortably in excess of the target of 350MPa, with good extrudability. These testing results also establish thatlower silicon contents do not provide adequate strength and highersilicon contents provide inferior strength and inferior extrudability.These testing results also establish that higher Mg contents result inan increase in extrusion pressure and inferior extrudability, withslightly inferior strength. The testing results further establish thatthe use of Mg and Si in ranges of 0.70-0.80 wt. % Mg and 0.85-0.95 wt. %Si achieve a particularly advantageous combination of strength andextrudability.

Several alternative embodiments and examples have been described andillustrated herein. A person of ordinary skill in the art wouldappreciate the features of the individual embodiments, and the possiblecombinations and variations of the components. A person of ordinaryskill in the art would further appreciate that any of the embodimentscould be provided in any combination with the other embodimentsdisclosed herein. It is understood that the invention may be embodied inother specific forms without departing from the spirit or centralcharacteristics thereof. The present examples and embodiments,therefore, are to be considered in all respects as illustrative and notrestrictive, and the invention is not to be limited to the details givenherein. Accordingly, while the specific embodiments have beenillustrated and described, numerous modifications come to mind withoutsignificantly departing from the spirit of the invention and the scopeof protection is only limited by the scope of the accompanying claims.

1. An aluminum alloy comprising Si and Mg in amounts within aquadrilateral defined by the following coordinates on an Mg/Si plot, inweight percent: I 1.15 Si, 0.70 Mg II 0.95 Si, 0.55 Mg III 0.75 Si, 0.65Mg IV 0.95 Si, 0.85 Mg

wherein the alloy further comprises, in weight percent: Mn 0.40-0.80 Fe0.25 max Cr 0.05-0.18 Cu 0.30-0.90 Ti 0.05 max Zr 0.03 max Zn 0.03 max B0.01 max

with the remainder of the alloy being aluminum and unavoidableimpurities in amounts of up to 0.05 wt. % each and 0.15 wt. % total. 2.The alloy of claim 1, wherein the Mg and Si are present in an Mg/Siratio of no more than 0.88.
 3. The alloy of claim 1, wherein the Mg andSi are present in an Mg/Si ratio of at least 0.69.
 4. The alloy of claim1, wherein the Mg and Si are present in an Mg/Si ratio of 0.69-0.88. 5.The alloy of claim 1, wherein the alloy includes excess Mg as defined bythe following equation:Excess Mg=Mg−(Si−(Mn+Fe+Cr)/3)/1.16 (all values in wt %).
 6. The alloyof claim 5, wherein the alloy includes up to 0.40 wt. % excess Mg. 7.The alloy of claim 1, wherein the alloy, after homogenization,extrusion, and artificial ageing, has a predominantly non-recrystallizedmicrostructure.
 8. (canceled)
 9. (canceled)
 10. The alloy of claim 1,wherein the alloy includes Mg in an amount of 0.60-0.80 wt. % and Si inan amount of 0.85-1.10 wt. %.
 11. (canceled)
 12. The alloy of claim 1,wherein the Si and Mg in amounts are within a quadrilateral defined bythe following coordinates on the Mg/Si plot, in weight percent: I 1.15Si, 0.70 Mg II 0.95 Si, 0.55 Mg III′: 0.80 Si, 0.65 Mg IV′: 0.95 Si,0.80 Mg.


13. An extruded product formed at least partially of the aluminum alloyof claim
 1. 14. An aluminum alloy comprising, in weight percent: Mg0.60-0.80 Si 0.85-1.10 Mn 0.40-0.80 Fe 0.25 max Cr 0.05-0.18 Cu0.30-0.90 Ti 0.05 max Zr 0.03 max Zn 0.03 max

with the remainder of the alloy being aluminum and unavoidableimpurities in amounts of up to 0.05 each and 0.15 total.
 15. The alloyof claim 14, wherein the Mg and Si are present in an Mg/Si ratio of nomore than 0.88.
 16. The alloy of claim 14, wherein the Mg and Si arepresent in an Mg/Si ratio of at least 0.69.
 17. The alloy of claim 14,wherein the Mg and Si are present in an Mg/Si ratio of 0.69-0.88. 18.The alloy of claim 14, wherein the alloy includes excess Mg as definedby the following equation:Excess Mg=Mg−(Si−(Mn+Fe+Cr)/3)/1.16 (all values in wt %).
 19. The alloyof claim 18, wherein the alloy includes up to 0.40 wt. % excess Mg. 20.The alloy of claim 14, wherein the alloy, after homogenization,extrusion, and artificial ageing, has a predominantly non-recrystallizedmicrostructure.
 21. (canceled)
 22. (canceled)
 23. The alloy of claim 14,wherein the alloy includes Mg in an amount of 0.70-0.80 wt. % and Si inan amount of 0.85-0.95 wt. %.
 24. An extruded product formed at leastpartially of the aluminum alloy of claim
 14. 25. (canceled)
 26. A methodcomprising: producing a billet of an aluminum alloy comprising: Mg0.60-0.80 Si 0.85-1.10 Mn 0.40-0.80 Fe 0.25 max Cr 0.05-0.18 Cu0.30-0.90 Ti 0.05 max Zr 0.03 max Zn 0.03 max B 0.01 max

with the remainder of the alloy being aluminum and unavoidableimpurities in amounts of up to 0.05 wt. % each and 0.15 wt. % total;homogenizing the billet at a temperature of 540-580° C. for 2-10 hours;and extruding the billet after homogenization to form an extrudedproduct.